The present invention is generally related to the field of wind speed measurement systems. In particular, the present invention is directed to an improved radar configuration having features that compensate for certain environmental factors in order to achieve an accurate wind profiling.
Conventional radar wind profilers typically are surface-mounted and direct a number of beams vertically or slightly off vertical. Signals are obtained from refractive index inhomogeneities in the clear atmosphere, or from particulates in the air. Because these scatterers often move with the wind, the signals returned to the pulsed radar are Doppler-shifted. By measuring the Doppler shift in the radar beams pointed in different directions as a function of time after radar pulses are transmitted, the horizontal and vertical wind vectors can be calculated as a function of height above the radar.
A conventional example of a wind profiling system uses triangular geometry as depicted in a 1961 IEEE article (Ed Sharp, IEEE Transactions on Antenna Propagations, AP-9, pages 126-129). The subject article, incorporated herein by reference, describes a triangular arrangement of planer-array antenna elements. The purpose of this arrangement is to reduce the number of antenna elements needed to obtain useful measurements.
Placement of wind profiling systems on moving platforms such as ships or planes create an additional level of complexity often leading to inaccurate systems. The only known 915 MHZ wind profilers that have been successfully operated on ships have mounted the radar""s antenna on a flat panel that is isolated from the ship""s deck by a mechanical 3-axis gyroscope, which mechanically stabilizes the panel with respect to the horizon despite ship motion. This arrangement is described in an article in The Bulletin of American Meteorological Society (No. 73, pages 1587-1592, by D. A. Carter, W. L. Ecklund, K. S. Gage, M. Spoward, H. L. Cole, E. F. Chamberlain, W. F. Dabberdt, and J. Wilson, 1992). This article is incorporated herein by reference, and describes the first test of a shipboard wind profiler. The mechanism described in the subject publication is expensive and large, and typically includes a large surrounding clutter fence to reduce sidelobe interference. The size of the installations has been in the range of 3.5 Lxc3x973.5 Wxc3x973 H (all in meters).
Signal interference through sidelobes on these shipboard installations severely degrades wind measurement products in the marine boundary layer below an altitude of 800 meters, an altitude range where accurate wind measurement is most needed. This situation is described from an article in the publication The Journal of Atmospheric and Oceanic Technology (No. 15, pages 826-834, by L. M. Hartten, 1998). This publication is incorporated herein by reference, and describes the reconciliation of surface and profiler winds at various types of sites.
The commercial antennas used in the installations of the above-cited publications are considered state-of-the-art. The design concepts behind these antennas are described in an article published in the IEEE Transactions on Antennas and Propagation (AP-31, 190-193, by J. Ashkenazy, P. Perlmutter and D. Treves, 1998). This article is incorporated herein by reference, and describes a modular approach for the design microstrip array antennas.
Most such radars in use today typically produce a change in beam direction by mechanically deploying different lengths of cable between the transmitter and a few antenna segments. They are incapable of switching quickly between radar pulses (spaced less than 1 ms apart) and can obtain only 3-5 different beam-pointing directions since each direction requires a different combination of cable lengths. Thus, such arrangements cannot easily compensate for platform motion e.g., on ships, planes and buoys. This is critical since some wind profiling systems may require the ability to move beams rapidly (every 100 ms) to any one of thousands of possible directions, depending on the instantaneous orientation of the moving platform.
For all radar antennas, particularly those only a few wavelengths in diameter, energy leaks out of the main beam on transmission. This energy leaks into the antenna from many undesirable directions on reception. These unwanted leaks, called sidelobes, cause interference to the desired atmospheric signals in the main beam which are often quite weak. As a result, the sidelobes severely degrade the quality of the resultant wind profile data.
Accordingly it is one object of the present invention to overcome the limitations of the conventional art, thereby providing a far more accurate and flexible wind profiling radar system.
It is another object of the present invention to provide a wind profiling system that eliminates the necessity of mechanical gyroscopes and other mechanical peripherals necessary in the conventional art.
It is a further object of the present invention to provide a wind profiling system that substantially compensates for environmental motion of the platform on which the system is located.
It is an additional object of the present invention to provide a wind profiling system that has side lobes that are substantially reduced compared to those of the conventional art.
It is yet another object of the present invention to provide a wind profiling system capable of handling rapid variations in environmental movement.
It is again another object of the present invention to provide a wind profiling system having a reduced size compared to conventional arrangements.
It is still an additional object of the present invention to provide a wind profiling system having a smaller xe2x80x9cfootprintxe2x80x9d and requiring less material than conventional systems.
It is again another object of the present invention to provide a wind profiling system that can be deployed in a nadir-pointing configuration on aircraft.
It is yet a further object of the present invention to provide a wind profiling system that can be easily mounted on a ship or open-ocean buoy.
These and other goals and objects of the present invention are achieved by a phased array antenna system having a plurality of transmit/receive radiator elements. These elements are arranged in a two-dimensional hexagonal configuration matrix.
Another aspect of the present invention is manifested by a method of operating a phased array antenna system having a plurality of transmit/receive radiator elements. The method of operation includes the step of applying power to the antenna radiator elements in a non-uniform manner.